Ripple Voltage [273]
The ripple voltage (Vr) is the peak-to-peak swing of a filtered
waveform.
IP
Anode
Forward
Operating
Region
Gate
Ripple
Reverse
Blocking
Region
Cathode
VR
IG3
VBR(R)
IG3 > IG2 > IG1
IG2
IG1 = 0
V
VBR(F) F
Forward Blocking
Region
Ripple
IR
Fig 13.22 – Silicon-controlled Rectifier
Fig 13.21 – Ripple Voltage
Vr =
IL t
c
where:
IL = dc load current
C = filter capacitance, in farads
t = time between charging peaks
t @ 16.67ms for H W rectifiers
t @ 8.33ms for FW rectifiers
Silicon Unilateral Switch [273]
The silicon unilateral switch (SUS) is a thyristor that is forced
into conduction when the forward voltage across the device
reaches a specified forward breakover voltage, VBR(F). Once
triggered, the device becomes a low-impedance conductor.
It remains in the on state (conducting state) until its forward
current (IF) drops below the holding current (IH) rating of the
device. At that time, the device returns to the off state (nonconducting state).
RMS Reverse Voltage [273]
The rating of a diode found by converting the peak repetitive
reverse voltage rating to an rms value (Vrms = 0.707Vpk).
Cathode
SCR
See Silicon-Controlled Rectifier.
VR
Silicon-Controlled Rectifier [273]
A Silicon-controlled Rectifier (SCR) is a three-terminal,
unidirectional device similar to the silicon unilateral switch.
A third terminal, called the gate, provides another means of
triggering the device. SCRs were designed primarily for halfwave ac control applications, such as motor controls, heating
controls, and power supplies; or wherever half-wave silicon
gate-controlled solid state devices are needed.
304
Chapter 13
IF
Anode
Reverse
Blocking
Region
Forward
Operating
Region
VBR(R)
VBR(F)
VF
Forward
Blocking
Region
IR
Fig 13.23 – Silicon Unilateral Switch
Diodes, Rectifiers, Thyristors
305